Filters used in for example bioreactors or fermentors need to be heated in order to remove condensed liquid to prevent them from clogging. In order to heat the filter it is suitable to enclose the filter by a filter heater. The filters may have inlet connection and outlet connections. The filter heater should be able to attach to the filter without disconnecting connecting tubes or other connections to the filter. Prior art filter heaters have been difficult to attach to the filter and furthermore the combination of filter, filter heater and tubes has been a bit bulky and not easily handled.